The doctor and Sarah-Jane are summoned to the world of Karn,which is within the jurisdiction of the time lords. After discovering a group of crashed rocket ships they than taken in a scientist named Solon and his assistant Condo. It isn't long before the doctor and Sarah are knocked out by Solon,who is seeking to use the doctors brain for one of his experiments. Meanwhile,a mystical group called the Sisterhood Of Karn have captured the TARDIS. Their experience with the time lords is clouded by an encounter with the villainous Morbius,who was intent on using their elixir,which they believe is created by a sacred flame of life,in order to allow every time lord to live forever. This elixir is now diminishing and the Sisterhood blame the doctor,who they apparently originally summoned While on the operating table of Solon,the doctor too is captured by the conjuring of the Sisterhood where he unsuccessfully attempts to plead that he is not of the same intention as Morbius and they prepare him for sacrifice for their diminishing elixir. By this time Sarah has escape from Solon. After disguising herself as one of the Sisterhood and helping the doctor escape,the Sisterhood attack her with a light ray that temporarily blinds her.
Solon returns to the sisterhood begging for the Doctor back. He wants the doctors brain to house that of Morbius who he possesses,and whom Sarah has already encountered. After the doctor and Sarah escape from Solon again,the disembodied brain of Morbius is convinced the doctor is sent by the time lords in an attempt to destroy him and demands Solon put him in a specialized body he'd created prematurely. During this time Solon finds the doctor and Sarah have returned,along with the Sisterhood now looking for the brain they now know Solon has. When Sarah's sight returns,she and the doctor are both accosted by the mutant body Morbius now inhabits. While a cyanide concoction of the doctors successfully kills Solon,it's the sisterhood chasing Morbius off a cliff that finishes the job. The doctor has been lethally injured in a time lord brain stretching session with Morbius and the Sisterhood leader Maren sacrifices herself to give the last of their original elixir to the doctor. Before departing with Sarah on the TARDIS,the doctor gives them a special material to keep the flame of life from going out again before leaving a midst big explosion.
Very much a story of this era of Doctor Who loosely modeled around a Hammer horror story,in this case Frankenstein,this story very much centers in on the obsession with eternal life-between the entropy it's caused for the Sisterhood and Karn society as well as the madness of Solon himself. No irony is lost that,even though Sara-Jane Smith spends the the middle parts of this serial blind,she manages to do more to save herself and the doctor than Solon or the Sisterhood are in their obsessions with survival at all costs. This story also features a lot of first hand information about time lord society,as well as the Sisterhood's clarity on the fact the doctor isn't the only one who sees the time lord's as having a mild streak of moral cowardice. One important scene is the brain stretching session before Morbius's death-where several other characters representing the doctor are shown following the face of William Hartnell's first. Not only does this indicate an unusual way of time lord interaction but that,just perhaps (though the faces could've represented the first doctor in younger states of his life),the doctor we first saw in An Unearthly Child may not have been the doctors first incarnation.